The Vatican has denied the Catholic Church covered up a case of a priest accused of molesting 200 deaf boys in the US from the 1950s to the 1970s.

It has been alleged the Vatican ordered a church trial of Father Lawrence Murphy be stopped, after the priest wrote a letter to Cardinal Joseph Ratzinger - now Pope Benedict.

Arthur Budzinski, 61, says he was repeatedly molested at the St John's School for the Deaf in suburban Milwaukee 40 years ago.

His daughter Gigi says it has had a huge impact on the whole family.

"We're happy that it finally got out there to the people. He fought for 37 years," she said.

"He met with members of the Vatican in 1974 and still nothing was done for him.

"It started when he was 12 years old. He reported it to many people - Milwaukee police, St Francis police, and no-one helped him. No-one helped him and his classmates and his friends."

As Cardinal Ratzinger, the future Pope was in charge of a Vatican department responsible for investigating cases of alleged abuse.

Successive archbishops in Wisconsin were aware of the allegations but did not act, and there was no criminal prosecution.

The Vatican was finally contacted in 1996, but the department which Cardinal Ratzinger oversaw decided not to take action.

Cardinal Ratzinger's deputy ruled that the alleged molestation occurred too long ago and the accused priest should instead repent and be restricted from celebrating mass outside of his diocese.

The Vatican says there was no cover-up because the cases are already in the public domain.

'Hurt and disappointed'

Meanwhile a group claiming to be clerical abuse victims has staged a press conference outside the Vatican, where they called on the Pope to explain why more was not done.

Peter Isely is a spokesman for the Survivors Network of Those Abused by Priests. He says Father Murphy was sexually assaulting children in the confession.

"We're Catholics from Milwaukee, Wisconsin and survivors. We need to hear from him [the Pope] - why he did what he did," he said.

"A man who raped and molested children in our archdiocese - we need to know why he did not let us know about him, why he didn't let the police know about him, why he did not condemn him, why he did not take his collar away from him."

Barbara Blaine is from the same group and says those affected are extremely distraught.

"[We are] hurt, disappointed, to learn that the church officials here - including the Pope - have actually been more concerned with protecting the privacy and reputation of child predator priests rather than the innocent children," she said.

The two say they were briefly detained by police outside the Vatican because they did not have a permit for a news conference.

The latest claims of a cover-up come just days after the Pope rebuked Irish bishops for their handling of half a century of sexual abuse of minors by clergy.